Below are some of the reasons why your ads may not be getting enough budget and corrective actions for the same -

ReasonProblemWhat to do next?
Campaigns / Adsets are not spending enough
This can mean that your ad is not competitive in the auction or there aren't enough results available in your target audience. 
Therefore Facebook stops ad delivery with consistency.

a. Try different creative. 

b. If the user can not resonate with the ad, it can make it challenging to spend the budget. Consider removing low-quality attributes from your ads or keeping track of ad relevance ranking. 

(Click here to understand ad relevance diagnostics)

c. You can also consider populating the creative in a different campaign 

Low performing ads
If an adset has too many ads running, this can mean that the creatives are not getting enough budgets to deliver. 

Consider pausing low performing ads 
(Click here to understand how creative insights on AdYogi platform can help on gaining insights in this situation)
Non- performing adsAn ad generally does not end up performing incase it does not get enough budget.a. This could be due to a low campaign budget. In such cases, consider increasing the overall campaign budgets and pause a few non-performing ads which have high spends. 
b. Another alternative could be to populate the ad in multiple campaigns.